Extend direct IPI support to x86 platforms that use CONFIG_X2APIC=y

[peter-mitsis]

Background:

It was reported in Issue #87046 that the addition of direct IPI support to x86 was causing regression failures on up_squared/apollo_lake boards.

It was observed that the up_squared/apollo_lake boards use CONFIG_X2APIC=y while the qemu_x86_64 board that was used for testing used CONFIG_X2APIC=n. This is relevant as the mechanism used to deliver IPIs is dependent upon this Kconfig option. To that end, x86 direct IPI support has been restricted to platforms that do not CONFIG_X2APIC (see PR #87068).

Describe the solution you'd like

Direct IPI support for x86 should be extended to support the case where CONFIG_X2APIC=y.